Custom Drag and Drop for importing .srt files
Not sure if you already looked through some of the older(around 2013-15) posts about whether it's possible to handle from python(it wasn't). The last thread I saw about implementing some way for handling drag and drop imports from python ended with nothing in 2015 (link). That same thread had drag and drop import for .obj files from somebody, but iirc it was in C. 

Rumor about it being in 2.8 is likely due to comment on similar post to yours here on stackexchange which didn't have any quotes/sources about it (link).

I think that rumor is based on the ability to drag and drop .blend files to open/link/append that's new to 2.8. I don't know if it will help, but there's a  developer thread about it, could be a starting point (link)